Actually an angel is an entity until they die then they become a spirit unless they are archangels or some other high ranking angels then they are immortals. Also to those who believe I don't think forming a relationship with an angel is recommended for many reasons. Why would an angel want to have a short term relationship with a human in the first place unless if you believe in reincarnation and are destined to live on in many lives then if an angel wants to they can make it so that in every life you live you will always be together. But angels aren't physically here and will never be so they shouldn't really replace a human being...

Marriage to a spirit is a tradition in some religions. The Vodou religion, for instance, holds this idea. Essentially, it's an important ceremony not taken lightly, meant to connect you strongly with a particular Lwa.

I know some reconstructed practices, such as Heathenism, also hold the idea of spirit marriages.

I haven't run across the idea in Hellenismos.

While yes, marriage is an institution created by humans, the religion and rituals attached to it are also created by humans. They're a form of communication between subtle being and physical being. A beautiful way in which we connect to our spiritual lives. So, it makes sense why some customs cross over into the spiritual.

We do the same now. Why would you clean negativity out of your home? Negative "energy" isn't physical. Why do it? Why give food and drink to a spirit? They are not physical, why bother cooking a meal for a spirit or deity.

The answer is simple. It's a way we already know how to communicate and show we care. It builds the bonds of kharis between two beings. In the case of magic, it's a way for us to connect/communicate what we do here in the physical to the spiritual.

So, yes, marriage to a spirit or deity is a thing. I wouldn't consider it a thing to be taken lightly, and I would never go into something without heavy contemplation. However, the meaning of this relationship would hold different for other people. Also, I do not think angels, as Abrahamic entities, fall under those ideas. Other "angels," I have no idea either. You might have better luck researching this on your own.

The archangels come up in the third triad there are many other types of angels above them the highest being the seraphim and those ones that are on top of the archangels are harder to really come into contact with than an archangel. Some archangels can actually form bonds with some humans, not necessarily romantic or marriage but companionship for sure. They are extremely busier though than regular angels and have many duties to attend to.

Well angels cannot marry they are there to intercede when we need help. (From a Christian point of view)
This one is for H2O:
Well in Vodou some Vodouwizans marry spirits this is called "Maraj Lwa" you marry the Lwa that proposes to you or some people go into relationship with spirits. Maraj Lwa are not done with every spirit. Maraj Lwa come with many benefits such as protection,the spirit will provide allot for their spouse and many more blessings. These are done when the lwa are in possession. Some women who marry one spirit has to marry another example if one marries Ogou Ferray they marry Damballah or another "cool" spirit so that the one who is getting married does not get a hot head. Allot the the times when someone would marry a "hot" spirit they would marry a "cool" spirit to keep their head balanced between the two you dont want a head that is too hot. Many times certain days are reserved for their spirit that they are married to like Freda most of the time is thursdays which people would not hug for show affection for other people and only exclusively for their spiritual spouse. Maraj Lwa are very common in Vodou.

Of course Angels can marry. Marriage isn't necessarily only a "human thing"; the word is, but the point of this is actually be with someone you truly love... Because humans marry it doesn't mean entities don't. Angels and all entities have feelings too-of course they can truly love an entity and marry them. Because they're entities it doesn't mean they can't feel love. However if you're looking for one to marry with you... Good luck.....

The idea behind marriage is to establish a legal union between two beings(usually humans), according to the law of the country these people reside. By doing so, each of the partners is aware of their legal rights and obligations between themselves and towards their children. Both people should have reached age of maturity (in most countries this is age 18) because they should be able to make an informed choice and give a consent. This requires them to be are separate beings with their own Free Will.

Angels cannot give consent or make an informed choice because they are presumably with no free will. One can also argue that they are not separate beings as we understand a separate being by human standard. All of the archangel names, when translated include one of the God's names. We can even assume that they are partially united with their source. I have also noticed, that angels have a shared conscious mentality, even the ones that are lower in the hierarchy and closer to humans. They are also directly linked to their source and cannot deliberately disobey it. They have been created to carry out certain tasks, including to pass down messages (in general), this is especially valid for the orders of angels and archangels, which are the ones that are meant to assist humans. Even these lower orders of angels are not very human alike, despite that they are depicted as humans with wings. Their most higher form looks more like beam of light. The angels of higher orders are believed to be even more strange looking in appearance. They are overall loving beings, but they were not created with the sole purpose to love and assist humans, and they certainly cannot go against the divine will and engage in marriages. Something which is totally out of their assigned duties. Besides, this union with human will create another issue with impartiality. Being in union with their spouse will almost automatically require of them to be partial and bias, when it comes to protecting the interest of their spouse. However, they are not to begin with impartial beings, since they are partially united with Divine. This will create very serious paradox, since they simply will be unable in some cases to accomplish both the task they have been created for and the task their partner requires them to do. A task that does not agree with the task they have been given by their Creator. They simply will never be able to just do your bidding. Which of course will create tension and issues withing the marriage. Most human beings will always want to control everything and fortunately not all beings can submit only to their will.

The Book of Enoch mentions that the so called "fallen angels" got involved with human women and in result giants were created. Nephilim these offsprings were called. Of course, these angels had Free Will. The Divine, obviously, did not agree with all this and dispatched archangels Raphael and Michael to capture all fallen angels and to deal with their offsprings. It is believed that the spirits of the giants shall haunt people until the last day. Pretty much these beings created of the union of flesh and spirit were extremely despised by both humans and Divine. Humans cried to God to save them from the giants, but ultimately their spirits were not allowed in heaven and they were left to roam the earth and to torment the very humans that rejected them. In conclusion, nothing good came from this union between humans and fallen angels, for neither of the sides involved. No one was a happy camper at the end, according to the book.